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Chapter 20: Q54P (page 984)

Draw the mechanism for the formation of β-lactose from a α- D-galactose and β- D-glucose in dil HCl.

Short Answer

Expert verified

Lactose, a disaccharide is a sugar made up of galactose and glucose subunits with the molecular formula C12H22O11. Lactose makes around 2-8% of milk. β-lactose is the beta anomer of lactose. It is a natural product found in Arisaema tortuosum and hypericum perforatum.

Step by step solution

01

Introduction

Lactose, a disaccharide is a sugar made up of galactose and glucose subunits with the molecular formula C12H22O11. Lactose makes around 2-8% of milk. β-lactose is the beta anomer of lactose. It is a natural product found in Arisaema tortuosum and hypericum perforatum.

02

Mechanism

As we can see that in the first step proton transfer occurs with HCl followed by the elimination of water. Now, nucleophilic addition of beta -D-glucose occurs at electrophilic carbonyl carbon of alpha-D-galactose. After this step occurs the deprotonation and thus, beta lactose is obtained. The raction mechanism can be represented as-

Mechanism of formation of β - lactose

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Most popular questions from this chapter

Question:Draw the mechanism for the acid-catalyzed hydrolysis of β-maltose.

An unknown disaccharide gives a positive Tollens’ test. A glycosidase hydrolyzes it to d-galactose and d-mannose. When the disaccharide is treated with methyl iodide and Ag2O and then hydrolyzed with dilute HCl, the products are 2,3,4,6-tetra-O-methylgalactose and 2,3,4-tri-O-methylmannose. Proposea structure for the disaccharide.

What are the systematic names of the following compounds? Indicate the configuration (R or S) of each asymmetric center.a. D-glucose b. D-mannose c. D-galactosed. L-glucose

Trehalose, C12H22O11, is a nonreducing sugar that is only 45% as sweet as sugar. When hydrolyzed by aqueous acid or the enzyme maltase, it forms only D-glucose. When it is treated with excess methyl iodide in the presence of Ag2O and then hydrolyzed with water under acidic conditions, only2,3,4,6-tetra-O-methyl-d-glucose is formed. Draw the structure of trehalose.

The aldaric acid of D-glucose forms two five-membered-ring lactones. Draw their structures.

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